There is a well-known method of treating cancer patients, etc. by irradiating a target volume in the patient's body with a charged particle beam (ion beam) such as a proton beam. The system used for the irradiation comprises a charged particle beam generator, a beam transport line, and a treatment room.
The charged particle beam accelerated by the charged particle beam generator reaches an irradiation nozzle (irradiation device) in the treatment room via the beam transport line. The distribution of the charged particle beam is broadened by the irradiation nozzle and an irradiation field suitable for the shape of the target volume is formed in the patient's body. The irradiation nozzle may also be equipped with a scanning device which performs the scanning of the charged particle beam in conformity to the shape of the target volume.
Incidentally, since precise irradiation becomes difficult when the target (e.g. target volume) moves due to the patient's respiration or the like, the gating irradiation (irradiating the target only when the target is at a preset position (in an extraction permission area)) is carried out.
In a conventional technology described in Patent Literature 1, the gating irradiation is performed by using a synchrotron as a charged particle beam generator that repeats the injection/acceleration/extraction/deceleration of the beam. The periodic cycle time of the injection/acceleration/extraction of the beam is controlled in order to effectively use the beam in the gating irradiation.